Educational apparatus



Dec. 20, 1933'.

S. STERN EDUCATIONAL APPARATUS Filed Dec. 8, 1936 3 Sheets-Sheet INVENTO R Sander stern ATTORNEY 5 Dec. 20; 1938.

s. STERN EDUCATIONAL APPARATUS Filed Dec. 8, 1936 5 Sheets-Sheet 2 .IIIIII.

INVENTOR 8ander'8l-ern W W ATTORNEY Patented Dec. 20,- 1938 J UNITED STATES PATENT OFFICE EDUCATIONAL APPARATUS Sander Stern, New York, N. Y.

Application December 8, 1936, Serial No. 114,726

16 Claims.

This invention relates to demonstration equipment particularly useful in illustrating the principles of electrical circuits.

' g The instruction of electricity is relatively diffi- 5 cult because it is an abstract science dealing with '1 invisible entities." Instruction and perception by the students ismaterially stimulated and enlii' tive effects in the closed operating circuit to simulate electrical measuring devices.

I It is accordingly the main object of my pres- -'ent invention to provide novel apparatus for demonstrating electrical circuits. 2o Another object of my present invention is to a .fiprovide novel means for setting up mechanical counterparts of a continuous electrical circuit.

A further object of my present invention is'to I provide novel apparatus for demonstrating elec- 5. trical circuits which permits ready re-arrangement to' simulate different circuit combinations. These; and other objects of my'invention will become apparent in the following description taken inconnection with the drawings, in which: 3 Figure '1 is a plan view of a preferred embodi- ;ment of my present invention shown arranged to represent the electrical circuit of Figure 2, which is .a'continuous direct current circuit. V I j Figures 3 and 4 illustrate markings on the cord connecting the several pulleys of the apparatus I f to represent the flow of current or electrons through the circuit. y

i I Figure 5 is an end view of the driving member 'representing the electromotive force of the circuit.

' .10 j 'Figure 6 is an end view of the impedance or rejsistive element of the circuit.

' Figure? is an end view of the voltage measur- 7 --ing; member of the circuit. 1 Figures is a direct current parallel circuit sim- "15 ulated by the arrangement of the apparatus illus- J y trat-ed in Figure 9. r

Figure 9 isa plan view of a form ofmy invention arranged to simulate a direct current circuit such as shown in Figure 8. I

V 5 0; I Figure 10 is a plan viewof apreferred embodigmenlt for mechanically simulating the series circuit of Figure 12.,

a "ing the a. c.electromotiveforce.

Figure 11 is the section taken along l ill of lifigure 10 showing details of the d iYQ ltpresents Figure 12 is the series a. c. circuit mechanically represented in Figure 10.

The demonstration equipment of my present invention is adapted to be mounted upon a board In containing an arrangement of holes ll regu- 5 larly arranged to receive pegs of the units to be supported in optional positions on the board ID. The various mechanical members may be arranged to simulate a variety of circuits as will be hereinafter described, and may be arranged at 10 difierent sections of the board l0.

Figure 1 is a plan view of the mechanical members arranged to simulate a direct current circuit. The various members are interconnected by a cord or suitable tape l2 having painted or otherwise 15 marked thereon, alternate dark and light areas to represent the electron flow of the electrical circuit. The rope I2 is endless, representing a continuous electrical circuit. Rope l2 passes around pulley I3 which is driven by the motor M to sim- .ulate an electromotive force or battery E. The

cord I 2 is accordingly motivated by pulley I3. Guide pulleys l5 and I6 are attached to the board I 0 at suitable points to guide the cord l2 in its continuous path. Members R1 and R2 are designed to impede the course of the cord [2 and represent resistive elements in the circuit.

The speed of movement of cord I 2 simulates the current flow in the circuit. The greater the mechanical motive power imparted to pulley I3, the greater the speed of cord I2. This is similar to the electrical circuit where a larger electromotive force or voltage produces a proportionately greater current flow, other circuit parameters remaining the same.

Figure 2 is the electrical circuit diagram represented by the arrangement of Figure 1. The battery e is simulated by the motor I4 driving the pulley E3; the resistors 1'1 and 12 being represented by the corresponding units R1 and R2 to be hereinafter described in more detail.

A section of the endless cord, rope or tape 12 is illustrated in Figure 3 showing the alternate dark and light sections I! and I8 which may, for example, be black and yellow or black and white or any other combination of colors to clearly show the flowing nature of the circuit. In Figure 4 I have. illustrated a modified form of the cord l2 showing numerous circular spots H! on the cord to present the actual electrons in the circuit. The'faster the cord l2, and hence electron counter-parts I move, the greater will be the current flow represented. The motive force for imparting movement to thecord I2 is accomplishedby the n E F g 5 effect of the members R1 and R2.

ure 1, the end View of which is illustrated in Figure 5. The motor M is preferably an adjustable speed direct current motor, the speed of which is controlled by the field rheostat 20. It is to be understood that any suitable type of motor or speed control therefor may be employed. A mechanical motor may also be used and my invention is not limited to the specific motor or speed control employed. A clutch 2| is used to start or stop the cord motion by the clutch lever 22 without disconnecting the motor M from the power lines.

Referring to Figure 5 which is an end viewof the motive unit E, the pulley I3 is driven by the suitable friction cone drive 232' l. The pulley I3 is preferably made of light weight material and is supported by rod 25 upon a base 26 which contains a suitable thrust bearing to permit ready rotation of the pulley l3 with a minimum of frictional or inertial resistance. The base portions and circuits of the various units contain bolts 21 which are inserted into the holes ll of board If) to rigidly support the units as will be understood. Although I illustrate bolts 21, it is to be understood that anysimple suitable supporting means may be employed such as pegs and the like.

The cord 12 is wrapped around the pulley l3 preferably once, as illustrated. The top portion of pulley !3 has pegs 2B projecting therefrom. These pegs are used'to support another driving pulley similar to l3 for a second circuit or to support a metallic unit 29 or more units which would add to the inertia of the circuit to represent inductance in the electrical analogy.

plate 34 co-acts with the under surface of pulley 30 and is controlled by crank lever mechanism 353B pivoted at pivot 31. The pivot 31 is supported on board l0 by bolt 34. The end 38 of lever arm 36 is attached to a spring 39 which is, in turn, gripped by support member 40 containing a plurality of pegs 4|. The spring 39 accordingly may be attached to any one of the pegs 4| in order to Vary the pressure of the brake member 34 against the pulley 30 to in turn vary the resistive Post 40 is set into base-board ill by bolt 42. It will now be evident that by attaching the corresponding end of spring 39 to a lower peg of the group 4 l, the pressure against pulley 30 will be increased, which serves to reduce the speed of the cord l2, simulating an increased resistance placed in the electrical circuit to reduce the current flow therein.

The E and R elements of the apparatus may be used to set up any combination of battery and resistance direct current circuit. By making moi tor ['4 a reversible motor, the effect of current reversal is made evident to the students.

By increasing the speed of the motor [4 through field rheost'atfZU, the effect of increasing the voltage 10f the circuit will become apparent by a proportionate increase in the speed of the cord l2 cora given setting of the field rheostat 20 (constant voltage) The cord I2 is wrapped around the var ious pulleys once and the equipment is adjusted'sothat the cord I2. is reasonably taut to provide smooth motion thereof. Increasing the brake pressure at any of the resistor units R will reduce the speed of the cord l2 by causing it to slip upon the drive pulley l3 at motive unit E. Similarly, slippage may occur at any of the resistor pulleys 30. The speed of rotation of the guide pulleys l5 and I6 is directly proportional to the speed of the cord l2 representing the current flow in the circuit. A revolution counter I shown in Figure 1 applied to the axis of either of the guide pulleys [5 or E6 will indicate their relative speed and correspondingly indicate the current flow of the circuit. The scale of the revolution counter I may be marked in inches of cord passed per second or in electrons flowing per second or arbitrarily in amperes.

The effect of inductance in an electrical circuit may be simulated by placing weighted pulleys or weights 2%] as shown in Figure 5. Weight 29 may be added to any of the pulleys by means of peg arrangements. The eifect of the inductive load upon the direct current circuit would be apparent 'ti'on, except for a slight resistance which the inductance imparts through bearing 25, simulating the small electrical resistance of all inductances.

The voltage of the mechanical circuit of my invention is preferably measured by means of a Prony brake arrangement V1 and V2 as shown in Figures 1 and 7. The Prony brake measures the torque or pressure at any point in the circuit by means of the unit V1 or V2 corresponding to the absolute voltage of the electrical analogy. By using two units such as V1 and V2 on opposite sides of an impedance element such as R1 illustrated in-Figure 1, the voltage difference or the voltage drop existing across the impedance element R is determined.

The pressure or voltage measuring units comprise essentially of a pulley mounted upon a brake wheel 45 supported upon a base 41 containing a thrust bearing for the support rod 48 which is supported on board In by bolts 49 (Figure 5). A brake band 50 together with the block 5| is attached to the brake arm 52 extending from the unit. The periphery of brake wheel is preferably made slightly concave to better hold the brake band 50. A peg 53 projects near the end of brake arm 52 and co-acts with projection 54 of the spring balance meter 55 whichrecords the force exerted against it by the V unit. Scale 55 is supported on base H] by bolts 56. Rubber pegs 51'are preferably used to prevent the brake arm 52 from oscillating. The reading of scale 55 is proportional to the force or pressure of the cord l 2 at that point and is preferably calibrated in arbitrary volt readings although other units may be employed.

By arranging units V1 and V2 as drawn in solid in Figure 1, the voltage drop or difference in potential between the two points may be calculated by subtracting the readings on the scales 55 and 55'. However, a single determination of the voltage difference may be determined by placing the V units as illustrated in dotted lines in Figure 1 to get the differential reading upon meter thefpluralityflof holes II. p The spotted cord I rangements are set up by unit E serving as the voltage source, units R1 or R2 serving as resistance elements, guide pulleys I5 and I6 set in positions to keep the cord I2 taut and voltage measuring units V or V1 and V2 disposed at points 'where voltage is to be determined. The current of the circuitis determined by a revolution counter-I applied to any'of the guide pulleys such as? I5 and I6. Increasing the speed of motive unit E by speed control represents. increasing the voltageof the circuit, giving corresponding increased V and I readings. Increasing the brake pressure against the pulleys 30 of the resistance .units R1 and R2 slows down the speed of cord I 2 and "accordingly reduces the current of the circuit. :.-Inductanceweights corresponding to 29 (Figure 5) simulates the effective inductance in the transient or starting-up state of the circuit.

It is to be understood that the resistors may be assembled in different arrangements and more or less resistors than those illustrated may be used. By releasing the brake pressure of member 34 against the R pulleys 30, the effect of the removal of the particular resistor from the circuit is simulated.

. In Figure 9 is illustrated a parallel circuit arirangement analogous to the electrical circuit of Figure 1;

fcircuits 6| and 62 arrangedone above the other Q with the motive source E2 being cornmonto both.

Two pulleys, 63 and one beneath itinot shown) are arranged upon the rod 64 driven by motor 65 in a manner similar to the driving of rod 25 by motor I4 in Figure 5. The guide pulleys 66 and 61 are used to guide the circuit corresponding to cord 6|. are corresponding pulleys arranged to guide the cord circuit 62 disposed beneath that of 6I. Guide pulleys 68 and 69 together withresistor unit Rs complete the circuit corresponding to T3 of the parallel arrangement. The other circuit corresponding to n extends beyond the T3 circuit andincludes guide pulleys I0 and II with the resistor unit R4.

In'the parallel circuit analogy inaccordance with my invention, both independent 'current flows are visible by the speed of cords 6| and 62 together at rates dependent upon the pressure applied to the individual brake units R3 or R4. By varying :individual changed. The currents and voltage readings for. the. parallel circuit analogy may be taken in a,

fthespeed of'motive unit E2 both currents are simultaneously and proportionately affected.

Changing the brake pressures on units R3 or R4 corresponds to variation in theresistances r: and 1'4" of: the electrical circuit (Figure 8) and the currents will be correspondingly manner hereinabove described in connection with the series circuit of Figure 1.

v ;Animportant modification of my invention resides in the simulation of alternatingcurrent circuits. The mechanical elements are bolted-or otherwise attached to the baseboard I0 having 'oorresp'onds to the cord I2 of the directcurrent modification However, in the alternating "cur- "nectedin series with thecontinuous closed or Beneath guide pulleys 66 and 61 endless cord I 00. A plurality of guide pulleys IOI define the path of the cord circuit I00 and keep the cord taut.

The alternating electromotive force E8..O. is obtained by motor drive I02 connected to a flywheel member I03 having spur gear teeth on its periphery, through a clutch I04. The fly-wheel I 03 is connected to crosshead I05 by crossarm I06. This arrangement serves to translate the rotative power of motor I 02 to rectilinear or linear osc'illatorymotion at the crosshead I 05. The crosshead I05 is directly attached to the cord Figure 11 is an end View taken along II-II of Figure 10 to further illustrate the connec tion between the fly-wheel I03 and the crosshead I05. Fly-wheel I03 is keyed to shaft I01 extending from clutch I04. Crosshead I05 slides horizontally in guide member I08 in a manner well known in the art. The ends of cord I00 connected to the crosshead I 06 are shown having lugs I09 to facilitate mechanical fastening thereof. The crossarm I06 is made up of two sections connected by an elastic member or spring IIO. A sleeve or housing III is provided for spring H0. The function of spring H0 is to transmit the oscillatory motion across the connecting rod I06 and also to permit fluctuations in the movement of the cord circuit I00 independent of the rotation of fiy-wheel I03 or motor I02. The purpose of the compliant connection H0 is to render changes in the impedance elements of the cord circuit I00 apparent in the corresponding changes in the movement of the cord I00.

A series of holes II2 having different radial positions with respect to the shaft I07 are made in the fly-wheel I03. The end II3 of connecting rod I06 may be attached to any one of the holes H2. The extent of oscillation of crosshead I05 depends upon the radial position of end 3' of connecting rod I06 upon fly-wheel I03; the closer end H3 is to the center of rotation I01, the shorter will be the movements of cross head I05. The variable position of end II3 upon fly-wheel I03 is used to simulate variable voltage conditions corresponding to the unit EN.

The speed of revolutions per second of motor I02 correspond exactly to the frequency or cycles per second of .the cord circuit I00, since when 'no reduction gearing is used, one oscillation of the cord I00 occurs per revolution of motor I02. The amplitude of oscillation of cord I00 depends upon the value ofthe electromotive force imparted to the cord circuit by cross head I05, and is dependent upon the relative position of connecting-rod end II3 upon fly-wheel I03. The movement of cord I00 simulates the flow of electrons in an alternating current circuit. The frequency of motion of the cord corresponds exactly to the frequency of the whole circuit.

By introducing mechanical mass to the cord trical circuit issimulated. Accordingly, for the mechanical equivalent L of inductance, I provide a weight II I, slidable in guide posts II5, and rigidly connectedto the cord I00 at terminals H6. The function of weight H4 is to increase the mass of the cord circuit I00 at the section it is introduced to simulate the correspending lagging effect of inductance for cur-- rent in 'an electrical circuit.

By'introducing a compliant or spring component inthe cord circuit I00, a mechanical equivalentC for an electrical condenser is had. Ac-

circuit I00, the effect of inductance in an eleccordingly, I provide a leaf-spring III, the fixed end of which is set into a post I I8 bolted to the baseboard I0. The free end of leaf spring I I1 is attached to cord I by a suitable member I I9. The oscillatory excursions of cord I00 deflect leaf-spring II! to the dotted positions I I'II indicated. The elastic effect of leaf-spring IN is to continuously tend to restore the cord I00 from its displaced position with respect to normal.

Figure 12 is a schematic electrical diagram corresponding to the electrical elements simulated in the mechanical arrangement of Figure 10. The alternating current voltage generator 63.0. corresponds to the reciprocating motive power Ea.c. resistance 7 corresponds to the resistive element R; the inductance I corresponds to the mass element L; and the condenser 0 corresponds to the spring element C. This circuit is a closed or series alternating current circuit, the electron or current flow of which is visually represented by the cord I00.

To further illustrate the electrical variations in the mechanical simulation, I provide means for recording these variations in various parts of the circuit and directly compare the results. A tape or band I20, preferably of paper, is passed at a constant rate transverse to the cord circuit I00 in the manner illustrated in Figure 10. A roll of paper band I is stored in compartment IZI, and a clockwork feed or synchronous motor mechanism is enclosed in member I22 to move band I20 at a fixed speed. A recording arm i23 is attached to weight H4 and is adapted to mark a record of its motion upon band I20. Similarly,

a recording arm I24 projects from connection II9 to leaf spring III to mark an independent record of motion of the portion of the circuit at C. The

oscillatory excursions of cord I00 is reflected in a wave record of the arms I23 and I24 upon continuously moving band I20. Curve ic represents the voltage or force condition of the circuit as drawn by arm I24 at the part of the circuit adjacent thereto. Curve i1 represents the voltage or force condition of the circuit at the part of the circuit adjacent thereto.

A reference time curve In is provided by stylus I23 connected to mechanism E0. Mechanism E0 is directly driven by motor I02 through fly-wheel I03 and stylus I23 records a reference curve In independent of any variations the electrical circuit corresponding to cord Z00. This device comprises a pinion I26 meshiitg with the spur teeth I21 out into the periphery of fly-wheel I03. The rotation of pinion I28 is transmitted to a small fly-wheel I28 through bevelled gearing I20. Fly-wheel I28 is connected to a crosshead I30 by connecting rod I3I. Stylus I is directly connected to a crosshead I by connecting rod I3I. Stylus I25 is directly connected to crosshead I30. The extent of movement of stylus I25 depends upon the position of the end I32 of connecting rod I3I upon fly-Wheel I28. The nearer rod end I32 is to the periphery of fly-wheel I28, the greater will be the amplitude of the reference curve Io. The frequency of the curce I0 is identical with that of the rest of the circuit since it is directly driven from the common motor I02. By maintaining the speed of motor I02 constant, the frequency of the records on band I20 will remain constant. Accordingly I prefer to use a synchronous motor for I02 although any other suitable motor may be employed. The amplitude of the reference time curve In is optionally adjusted by suitably positioning of rod end I32 on flywheel I28 in a manner similar to the position of rod end I I3 of rod I03 as shown in Figure 11.

By varying the magnitude of the impedance elements connected in the cord circuit I00 corresponding phase displacements will occur in curves 2'0 and S with respect to the fixed reference curves In as will be understood by those skilled in the art. The variation in L of the circuit may be effected by either changing the Weight H4 or by adding to or subtracting from the weight I I4 by pegged attachments to weight I I l.

The instantaneous velocity of the cord I00 corresponding to the value of the effective current in the circuit may be accomplished by a ball governor device schematically indicated at I33. A pulley I34 is connected to the cord circuit I00 and oscillates a ball governor I34 with device I33. Variations in the velocity of cord circuit I00 are transmitted to stylus I projecting from device I33 which records a curve H on band I20. Curve H corresponds to instantaneous current at the portion of the cord circuit to which measuring device I33 is attached.

Although I have illustrated a mechanical ball governor device for obtaining the instantaneous velocity or current curve H in order to illustrate the phase displacement relations of the circuit, it is to be understood that other instantaneous cord velocity measuring devices may be substituted therefor. A bi-polar generator having a uniform flux field distribution may be connected to pulley I34 in place of ball governor device I34. The output of the bi-polar generator may then be connected to a recording galvanometer by connection leads to the generator rotor with slip rings. The recording galvanometer will then have a stylus similar to I35 actuated thereby to trace the instantaneous current curve H. v

The effective voltage or pressure at any portion of the cord circuit I 00 may be measured by means of measuring device V attached to the cord at a small crosshead I36. The crosshead I33 assumes the vibrations of the cord I00 riding in a guide I31. The oscillations of crosshead I33 causes a brake wheel I38 to rotate through connecting rod I39. Brake wheel I38 is connected to brake arm I40 through a brake band (not shown but similar to the Prony brake device V1 or V2 of Figure l) The end I iI of brake arm I30 is pressed against Y a scale I 32 which. measures the pressure at the end I M of arm M0. The effective pressure reading of scale M2 corresponds to the effective voltage at the portion of the circuit at which the meter V is connected into the circuit spring I43 is preferably inserted in the arm I30 to effectively synchronize the meter V system with the cord circuit I00 in a manner similar to the application of spring M0 to the EM. device.

Although I have described preferred apparatus for carrying out my invention, it is to be understood that variations and modifications may be made by those skilled in the art, and accordingly I do not intend to be limited except as set forth in the following claims.

I claim:

l; A device for mechanically simulating a continuous electrical circuit including an endless substantially inextensible rope for representing the electrical circuit, and means for guiding said rope to define the closed path of said rope; and means for driving said rope comprising a series wound direct current motor, whereby the char- .ly simulated.

-2. A device for mechanically simulating a continuous electrical circuit including an endless substantially inextensible rope for representing the I electricalcircuit, and means for guiding said rope to define the closed path of said rope and hold said -rope-taut'; and means'for driving said rope comprising and adjustable speed motor, whereby different voltage conditions in the circuit may be simulated.

, 3. ,A device for mechanicallysimulating a continuous electrical circuit including an endless substantially inextensible cord for representing'the motor, whereby different voltage conditions in the circuit may be simulated, and a first pulley driven by said motor, said cord being wound about said first pulley in a manner to enable slippage of the cord on the pulley; and means forimpeding the motion of said cord to simulate a resistance element in the circuit comprising a second pulley coacting with said cord, and means for braking the rotation of said second pulley including a brake-shoe operable against said second pulley.

' 5; A device for mechanically simulating a direct current electrical circuit including an endless substantially inextensible cord for representing 1 the electrical circuit, and means for guiding said cord-to define the closed path of said cord and hold said cord taut; means for driving said cord comprising a series wound direct current motor, whereby the characteristic action of direct current'circuits is closely simulated; and means for impeding the motion of said cord to simulate a resistance element in the circuit comprising a pulley coacting with said cord, means for braking the rotation of said second pulley including a brake shoe operable against said second pulley,

and, means for adjusting the pressure of said brake shoe against said second pulley. 5o

6. Ina device of the type described, the combination of an endless substantially inextensible 1 rope 'for representing anelectrical circuit, and

means for guiding said rope to define the path of said rope; means for driving said rope; and means for measuring the motive forces at a point in the 'rope circuit tosimulate voltage thereat.

' 7. In combination, an endless substantially inextensible rope for representing an electrical circuit, and means for guiding said rope to define the path of said rope; means for driving said rope;

1 means for impeding the motion of said rope to simulate a resistance element in the circuit; and

means for measuring the motive force at a point in the rope circuitto simulate voltage thereat.

' 8'. In combination, an endless substantially inextensible rope for representing an electrical circuit, and means for guiding said rope to define the path of said rope; means for driving said rope; means for impeding the motion of said rope to simulate a resistance element in the circuit; and means for measuring the motive force at a point in the rope circuit to simulate voltage thereat comprising a pulley rotatable by said rope, a

prony brake system having a lever, mechanically connected to said pulley, and means for measuring'the pressure at the projecting end of said lever.

9. A device for mechanically simulating a continuous electrical circuit including an endless substantially inextensible rope for representing the electrical circuit, said rope having spotted markings to represent electrons of the circuit, and means for guiding said rope to define the closed path of said rope and hold said rope taut; means for driving said rope comprising an adjustable speed motor, and a first pulley driven by said motor, said rope being wound loosely about said first pulley to permit slippage thereof; means for impeding the motion of said rope to simulate a resistance element in the circuit comprising a second pulley coacting with said rope, means for braking the rotation of said second pulley including a brake shoe operable against said second pulley, and means for adjusting the pressure of said brake shoe against said second pulley; means for measuring the motive force at a point in the rope circuit to simulate voltage thereat comprising a third pulley rotatable by said rope, a Prony brake system having a lever mechanically connected to said third pulley, and means for measuring the pressure at the projecting end of said lever; whereby the speed of movement of said rope is proportional to the magnitude of the electrical current flow represented, and is directly measurable by a determination of the speed of revolution of said rope guiding means.

10. A device for mechanically simulating a continuous electrical circuit including an endless substantially inextensible rope for representing the electrical circuit, said rope having spotted 'markings to represent electrons of the circuit,

and means for guiding said rope to define the closed path of said rope and hold said rope taut; means for driving said rope comprising a series wounddirect current motor, and a first pulley driven by said motor; means for impeding the motion of said rope to simulate a resistance element in the circuit comprising a second pulley coacting with said rope, means for braking the rotation of said second pulley including a brake shoe operable against said second pulley, and means for adjusting the pressure of said brake shoe against said second pulley; means for measuring the motive force at a point in the rope circuit to simulate voltage thereat comprising a third pulley rotatable by said rope, a Prony brake system having a lever mechanically connected to said third pulley, and means for measuring the pressure at the projecting end of said lever; means for increasing the inertia of the rope circuit to simulate inductance of the electrical counterpart comprising a cylindrical weight attachable to and rotatable by one of said pulleys whereby the speed of movement of said rope is proportional to the magnitude of the electrical current fiow represented, and is directly measurable by a determination of the speed of revolution of said rope guiding means.

11. A device for mechanically simulating an alternating current electrical circuit including an endless substantially inextensible cord system, means for guidingsaid cord to define the path of said cord; and means for oscillating said cord comprising a motor and a device for translating the rotative power of said motor into linear oscillations at said cord.

12. A device for mechanically simulating an alternating current electrical circuit including an endless substantially inextensible cord system, means for guiding said cord to define the path of said cord, andhold said cord taut; and means for oscillating said cord comprising a motor and a device for translating the rotative power of said motor into linear oscillations at said cord including a flywheel, acrosshead connected to said cord, and a cross-arm connecting said crosshead to said flywheel, said cross-arm having an elastic section in series between said flywheel and crosshead to permit cord fluctuations independent of said motor.

13. A device for mechanically simulating an alternating current electrical circuit including an endless substantially inextensible cord system, means for guiding said cord to define the path of said cord, and hold said cord taut; and means for oscillating said cord comprising a motor and a device for translating the rotative power of said motor into linear oscillations at said cord.

14. A device for mechanically simulating an alternating current electrical circuit including an endless substantially inextensible cord system, means for guiding said cord to define the path of said cord, and hold said cord taut; means for oscillating said cord comprising a motor and a device for translating the rotative power of said motor into linear oscillations at said cord; and means for simulating an inductance comprising a weight connectible in series with said cord.

15. A device for mechanically simulating an alternating current electrical circuit including an endless substantially inextensible cord system, means for guiding said cord to define the path of said cord and hold said cord taut; means for oscillating said cord comprising a motor and a device for translating the rotative power of said motor into linear oscillationsat said cord; means. for increasing the inertia of the rope circult to simulate inductance of the electrical counterpart comprising a weight connectible in series with said cord, said weight having a guide, and being slidable therein; compliant means connectible to said cord to simulate capacitance in the circuit comprising a leaf spring, one end of which is securable to said cord; and means for comparatively recording the excursions of said Weight and yielding means connections comprising a band movable across said cord circuit and stylii individual to said connections for marking on said band.

16. A device for mechanically simulating an alternating current electrical circuit including an endless substantially inextensible cord system, means for guiding said cord to define the path of said cord, and hold said cord taut; means for oscillating said cord comprising a motor and a device for translating the rotative power of said motor into linear oscillations at said cord including a flywheel, a crosshead connected to said cord, and a cross-arm connecting said crosshead to said flywheel, said cross-head having an elastic section in series between said flywheel and crosshead to permit'cord fluctuations independent of said motor; compliant means connectible to said cord to simulate capacitance in the circuit; means for simulating an inductance comprising a weight connectible in series with said cord; means for comparatively recording the excursions of said weight and yielding means connections comprising a'band movable across said cord circuit and stylii individual to said connections for marking on said band; and mechanism for providing a reference marking on said band comprising a reciprocating stylus geared to said flywheel.

SANDER STERN. 

